Many objects, such as defined above, contain items of significant value and/or of a sensitive or proprietary nature such as to be inviting targets for intrusion by thieves, terrorists, spies and the like. In all too many instances, conventional security equipment to help prevent these intrusions is ineffective, too dangerous for normal use around authorized personnel, and/or is too expensive for the degree of security provided. Also, the use of armed guards or security personnel is very expensive, and in some instances, may be unreliable in the face of an intense attempted intrusion.
It has been previously proposed that certain types of combustible materials could be used as delay barriers in helping to prevent unauthorized entry into various objects. For example, U.S. Pat. No. 888,052 to Vaughn et al. discloses a burglarproof jacket for a safe or vault having inner and outer casings, with a coating of plaster containing an ignitable material such as match heads, as well as explosive material, between the casings. While this construction for a safe may be an effective deterrent to an intruder, the explosive nature of some of the materials renders the safe hazardous in the normal workplace and poses a real risk of destruction of the contents of the safe. Furthermore, since combustion is so rapid, an intruder could simply wait until combustion has ceased and then gain entry to the object.
Also, U.S. Pat. Nos. 1,805,610 and 2,012,453, to Young and Lowy et al., respectively, disclose vault and safe constructions which include a gas producing combustible material to help prevent entry into the safe when the safe wall is cut with a torch or the like. The gas produced by the combustible material is intended to be physically incapacitating to the user of the torch. The clear disadvantage of these safe constructions is that the incapacitating effect of the generated gas can be easily circumvented by the use of a gas mask or other gas protection equipment. Also, the combustion is not self-sustaining and it is possible to quench the combustion with conventional fire extinguishing materials such as water.